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Chemical and physical processes for nano particles synthesis Process : Aerosol process - flame hydrolysis Aerosil process Degussa 1942 - synthesis of silica chemical reactions : H2 + O2 2 H2O SiCl4 + 2 H2O SiO2 + 4 HCl SiCl4 + 2 H2 + O2 SiO2 + 4 HCl silicon tetra chloride „ fumed silica“ principle : SiCl4 separation : air cyclone electrostatic filters fabric filters H2 O2 production in flame reactor particle size range : primary particle size 7 – 40 nm, spherical, amorphous particle powder as agglomerated particles of high porosity specific surface area 50 – 400 m2 / g product : titanium dioxide , aluminium oxide, zirconium oxide, zinc oxide Aerosol processes Images (transmission electron microscopy) of different oxides, produced by direct oxidation in an arc Particle formation in aerosol processes supersaturated vapour : reaction A(g) nucleation B(g) growth coagulation separation °°°° Gas to particle conversion GPC solution of precursor : droplet generation solvent evaporation intraparticle reaction Particle to particle conversion PPC separation Particle morphology during flame hydrolysis particle concentration aggregation particle growth temperature Chemical and physical processes for nano particle synthesis process : aerosol process - flame hydrolysis synthesis of titanium dioxide - chlorine process chemical reaction : 1000 – 1300 °C TiCl4 + 2 H2O TiO2 titanium tetra chloride 1000 – 1300 °C 4 HCl + + 4 HCl titanium dioxide O2 2 H2O + 2 Cl2 O2 TiO2 + 2 Cl2 hydrogen chloride TiCl4 + titanium dioxide principle : apparatus for titanium dioxide powder particle size : 100 - 400 nm, amorphous particles, product of anatase / rutile, part of rutile increases with temperature advantage products : : minimum aggregation and high dispersity of powder titanium dioxide, zirconium dioxide Chemical and physical processes for nano particle synthesis process : aerosol process – powder synthesis using laser light synthesis of silicon carbide and silicon nitride chemical reaction : SiH4 + CH4 SiC 4 H2 silicon carbide silicon hydride 3 SiH4 + + 4 NH3 Si3N4 silicon hydride + 12 H2 silicon nitride principle : vacuum pump, filter reactive zone KCl - window KCl - window laser argon reactive gas Reaction chamber for powder synthesis using a laser advantage : particle of high purity , monodisperse particle size distribution, exact stoichiometry disadvantage : precursor has to absorpt laser light only on a laboratory scale, mass produced 1 – 100 g Methods for powder generation with spray processes methods starting material process steps spray drying suspension solvent evaporation spray drying solution solvent evaporation, crystallization spray calcination suspension solvent evaporation, calcination spray decomposition solution of inorganic salts solvent evaporation, calcination spray hydrolysis non aqueous solution or hydrolysis by water vapour, for solutions liquid metal compound solvent evaporation solution or melt of metal thermal decomposition, for solutions organic salts solvent evaporation solution solvent evaporation and nucleation / spray pyrolysis plasma evaporation of solutions crystallization in a gaseous phase Spray hydrolysis chemical reaction : hydrolysis Ti(OC2H5)4 + TiCl4 particle : 2 H2O TiO2 + 4 C2H5OH 2 H2O TiO2 + 4 HCl + mostly non agglomerated, spherical particle with high purity hollow and porous particle can be formed easily controlling of powder porosity by concentrations in droplets and by temperature gradients droplets formation of nonporous particle crust formation dry particle nonporous particle dry particle densification nonporous densified particle porous and hollow particle Formation of nonporous and porous particle by spray hydrolysis